Internal combustion engines contain a crankcase, which typically houses many of the internal workings of the engine such as the crankshaft, cams, counterweights, and various gears. The crankcase is also used to collect and hold the oil or other lubricant used in the engine. The accumulated oil is transferred from the crankcase, typically through an oil filter, is delivered to various engine parts for lubrication, and is then returned to the crankcase.
Many engines currently use splash lubrication and/or rolling element bearings to deliver oil from the crankcase to the various engine parts. These methods are typically used because they are fairly simple and avoid the complexity of full pressure oil circuits. However, the disadvantage of these methods is that they do not have the capacity of full pressure oil circuits and typically suffer from higher wear. Therefore, it is desirable to use a full pressure oil circuit to maintain the capacity and durability of the oil delivery system.
A full pressure oil circuit typically delivers oil from an oil pump to various engine parts under pressure. In order to do this, the circuit that the oil follows must be enclosed as to maintain the oil under pressure throughout the oil circuit.
One way to create a full pressure oil circuit in an internal combustion engine is to create passages within the crankcase itself. Two designs for this type of oil circuit are disclosed in U.S. Pat. No. 4,285,309, which issued on Aug. 25, 1981, to Rolf A. G. Johansson, and U.S. Pat. No. 4,926,814, which issued on May 22, 1990, to Kevin G. Bonde. In both of these patents, there are passages integral to the crankcase itself.
In the Johansson patent, channels are made in the upper surface of the crankcase. Similarly, in the Bonde patent, multiple walls are formed in the top wall of the crankcase defining multiple channels. In both patents, the channels are then enclosed when the crankcase is assembled with an upper housing forming multiple passages. However, the designs in both the Johansson and the Bonde patents have certain disadvantages. In particular, if the upper housing and the upper surface of the crankcase do not fit perfectly, there will be some leaking of the oil. In these designs, any oil that leaks will leak out of the crankcase and be lost.
Another disadvantage is that the channels in both designs must either be machined into the upper portion of the crankcase or be molded integral with the crankcase. If the channels are machined, at least one additional step is added to the manufacture of the crankcase, which costs extra time and expense. If the channels are molded integral with the crankcase, the die for the crankcase becomes more complicated and costly and may require die-slides that will increase the cost of the die itself and will not allow dies for multiple parts. In addition, once the basic shapes of the channels are formed, there may be additional machining steps required to complete the full passages.
One way to overcome these disadvantages is to create passages within the crankcase cover rather than the crankcase itself. By having the passages in the crankcase cover, any oil that may leak from the passages is returned to the crankcase rather than leaking out of the crankcase and being lost. In addition, the manufacture of the crankcase itself is not complicated by requiring large upper surfaces, extra machining steps, or complicated and inefficient die molds.
One common way to create passages with a cover is to use oil tubes that are cast directly into the cover. However, molding a cover using cast in oil tubes is an extremely complex process, is expensive, and can lead to poor quality such as porosity around the oil tubes. In addition, once the cover has been cast with the oil tubes, the cover requires extra machining to eliminate any burrs on the oil tubes and many designs require extremely long drillings in order to complete the full oil circuit. Finally, the mold dies required for crankcase covers with cast in oil tubes are typically expensive and complicated because they require die-slides, they do not allow for molding multiple parts on a single die tool, and the molding procedures are complicated.
It would therefore be advantageous if a crankcase cover could be designed that contained passages that allowed the use of a full pressure oil circuit without the use of cast in oil tubes. In particular, it would be advantageous if the crankcase cover was easily manufactured, without the need for extra machining steps or long drillings, and could be manufactured with simple mold dies which do not include die-slides and allow for the manufacture of multiple parts on a single mold die to simplify and reduce the cost of the manufacture of the cover.